Dbvisit Replicate does not rely on any NLS variables to function properly.
It does not depend on any NLS setting in the user's environment. Rather, it overwrites NLS_LANG at the session level and so should not depend on any implicit conversion, meaning that it is not affected by any other environmental settings.
The value of APPLY.NLS_LANG AMERICAN_AMERICA.AL32UTF8 is used to set the environment variables.
Dbvisit Replicate uses APPLY.NCHARSET to understand what NCHARSET the source database is using, either UTF-8 or UTF-16. Dbvisit Replicate will then convert the data to match the target NCHARSET.
With the non Oracle database (MySQL and MSSQL), the connections are set to use Unicode only (UTF-8 for MySQL and UTF-16 for MSSQL) - and then the data is converted according to NCHARSET to the format expected by the target db connection.